The present invention concerns an improved hydraulic tappet, which besides being especially suitable for application to diesel engines also proves advantageous for normal internal combustion engines.
As is known, in some diesel engines the distribution shaft (cam shaft), in addition to having cams acting by sliding against the disk of the hydraulic tappet associated with each poppet valve head (or stem), also has a second series of cams. Each cam of this second series of cams is rotationally displaced relative to the respective cam for controlling the engine poppet valve. The second cams indirectly control the diesel fuel injectors at the proper time by means of a rocker arm.
The actuation of the diesel fuel injectors constitutes a further load on the camshaft, subjecting it to a downward deflection, which also influences the functioning of the cam that is supposed to actuate the cylinder poppet valves arranged on the same shaft. Such a deflection of the cam shaft results in an irregular opening of the valves and, consequently, a poor functioning of the engine.
In fact, the conventional hydraulic tappet, by its construction, is unable in certain cases to follow, with sufficient speed, the "lift loss" of the hydraulic tappet which, instead of causing the valve to open, collapses by virtue of the size of the deflection of the camshaft. It should be understood that as used herein and in the appended claims, the term "lift loss" will mean and include the lost motion which occurs within the tappet as a result of the deflection of the injector cam, so that the engine poppet valve doesn't open.